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MTTL, Mean Time To Learn

BusinessPractitioner

Simulator: the MTTR business case

For: team managers · finance, risk and compliance · executives and CIOsPrerequisites: Know what MTTD and MTTR measure.

Reading mode

An observability project rarely justifies itself; it is justified by what it changes in the duration and cost of incidents. This simulator links four quantities to a return on investment, with its assumptions in plain sight. Leadership knows these quantities or can estimate them: number of incidents, cost of an hour of downtime, mean time to detect or MTTD, mean time to restore or MTTR.

Incidents
Cost of one hour of downtime (major incident)
Detection and restoration times
Observability investment

Result

Annual incident cost, before
Annual incident cost, after
Annual gain
Annual return on investment
Payback period
Sensitivity: if the improvement is only 50%
Annual incident cost, broken down
  • Detection
  • Restoration
Cumulative over 36 months
  • Cumulative investment cost
  • Cumulative gains

Deliberately simple model: the cost of an incident is proportional to its total duration (MTTD + MTTR, MTTR being counted here from detection); a minor incident costs a fixed fraction of a major one; the investment does not reduce the number of incidents (a cautious assumption). Gains rise linearly during ramp-up. Costs are not discounted. Replace every assumption with your own figures.

Things to try

Section titled “Things to try”
  1. The starting case: 24 incidents a year, one in four major, MTTD brought down from 30 to 10 minutes and MTTR from 120 to 60 minutes. The annual gain exceeds €290,000 for a cost of €150,000 a year: the return is about 94% and the investment pays back in a little under 10 months.
  2. Sensitivity: look at the “if the improvement is only 50%” tile. The return turns slightly negative: the project only holds if you get more than half of the promised improvement. That is the question to ask before signing.
  3. The weight of revenue: set lost revenue to 0 (an internal service, for example). With only productivity and penalties, the gain no longer covers the cost: the business case depends entirely on what an hour of downtime really costs.
  4. Detection or restoration? Set the target MTTR to 120 minutes so that only MTTD improves. The gain drops to about €73,000. In this case detection accounts for only a fifth of the cost: restoration (diagnosis, correlation, runbooks) carries most of the gain. For a service prone to silent failures, detected late, it would be the other way round.

The rule to remember

Section titled “The rule to remember”

An honest business case does not present a single return figure but a range. It covers the target case, the 50% case and the improvement threshold below which the investment does not pay back. The assumptions (hourly cost, share of major incidents, expected gains) must be written down and owned by someone accountable for them. Review them after a year against the MTTD and MTTR actually measured.

Going further: the business dimension, the bridges between dimensions, the generative AI economic exposure calculator and the error budget simulator.